Exothermic and endothermic reactions such as Fischer-Tropsch synthesis (FTS), methane steam and dry reforming, methanation, methanol synthesis, and combustion reactions are important reactions for the production of valuable chemicals. So far, catalytic reactions have been widely investigated in fixed-bed and fluidized bed reactors with conventional catalytic materials. The packed-bed reactor is the most commonly used reactor type. The main disadvantages of a packed bed reactor are formation of hot spots in the catalyst bed and heat management problems (heat transfer limitation etc.). The hot spots lead to sintering and carbon deposits which result in a decrease in the amount of active sites. Besides the abovementioned limitations, pressure drop and mass transfer are limiting parameters for an efficient reaction.
In recent years, structured catalytic reactors draw a great interest for overcoming the above-mentioned limitations (mainly temperature regulation limitation, scale up limitation due to poor temperature control, catalysts deactivation and pressure drop). One of the examples is the use of the metal based structured catalysts such as metallic monoliths made by additive manufacturing due to their better heat transfer properties. These materials are made of micrometre-sized highly conductive fibers in which various reactive materials including catalysts are immobilized. Micro fibrous materials enable temperature control and provide uniform temperature profile for a range of highly endo/exothermic chemical reactions. One advantage of structured monoliths is that the porosity and pore size distribution can be controlled. This is in contrast to e.g. packed bed or foam materials, which have an inherent large pore size distribution.
It is known from US 2011/0129640 to Beall et al., 2 Jun. 2011 to make highly porous three dimensional (3D) ceramic articles from 3D powder printing. The articles can have apparent porosities from about 48% to 67% and can be used for flow applications. The 3D article can be constructed having a wall (e.g., solid, porous, or skinned), a honeycomb-like interior having macro porosity that can have, for example a porous lattice spacing that has graded or graduated dimension that decrease from larger cells at the periphery to smaller cells near the center which can create a radial profile to counteract peripheral pressure drop. The document describes that such graded structure can be used to level or equalize the flow front resulting in improved utilization of catalyst or radial ash distribution in such flow applications.